Previously proposed partitioning methods for partitioning a metal tube into two or more airtight regions along a longitudinal direction thereof, or partitioning an end portion of a tube that opens at least at one end thereof, include the crimping process that after a partitioning plate is inserted in the tube until a predetermined location along the longitudinal direction thereof, the tube is formed to be airtight by the crimping process. The crimping process has the advantage that no property change of the tube occurs with heat as is accompanied by the welding process, but has the disadvantage of being inferior in air-tightness. To eliminate this disadvantage, prior art proposes, in general, an attempt solution that an O-ring is fitted around an outer edge of the partitioning plate to improve air-tightness of the tube (Cf. Patent Document 1, for example). However, this method described by Patent Document 1 involves the step of indenting the outer edge of the partitioning plate to receive the O-ring, in addition to the steps of inserting the partitioning plate in the tube and fixing it in the tube by the crimping process, thus causing cost increase.
Further, prior art proposes an alternative attempt to provide improved air-tightness by the crimping process, according to which after a partitioning plate of steel product which is a representative example of metals is fixed in the tube of the steel product through the use of the shrinking effect of the tube produced by the crimping process, the tube is strikingly pressed against the partitioning plate from a surfacewise direction of the partitioning plate, to produce indentation extending along a peripheral edge of the partitioning place (Cf. Patent Document 2, for example).
This method described by Patent Document 2 can provide improved air-tightness by the crimping process, but involves the step of strikingly pressing the tube against the partitioning plate from the surfacewise direction of the partitioning plate, in addition to the steps of fitting the partitioning plate in the tube and fixing it in the tube by the crimping process, thus still suffering from cost increase.
Also, as is known from Patent Document 3, prior art proposes another alternative attempt that the coining process is taken to produce a sealing relationship between the tube and the partitioning plate. However, this method provides an increased number of processes by the extent corresponding to the coining process, thus causing cost increase.
Patent Document 1: Pamphlet of International Publication No. WO01/74633;
Patent Document 2: JP Laid-open (Unexamined) Publication No. 2001-212632; and
Patent Document 3: JP Laid-open (Unexamined) Publication No. 2002-12125.